1. Field of the Invention
The present invention relates generally to the design and use of medical devices, and more particularly to the design and use of an implantable port assembly for establishing extracorporeal blood circulation for hemodialysis and other blood treatments.
Access to a patient's vascular system can be established by a variety of temporary and permanently implanted devices. Most simply, temporary access can be provided by the direct percutaneous introduction of a needle through the patient's skin and into a blood vessel. While such a direct approach is relatively simple and suitable for certain applications, such as intravenous feeding, intravenous drug delivery, and which are limited in duration, they are not suitable for hemodialysis and other extracorporeal procedures that must be repeated periodically, often for the lifetime of the patient.
For hemodialysis and other extracorporeal treatment regimens, a variety of implantable ports have been proposed over the years. Typically, the port includes a chamber and an access region, such as a septum, where the chamber is attached to an implanted catheter which in turn is secured to a blood vessel. In the case of veins, the catheter is typically indwelling and in the case of arteries, the catheter may be attached by conventional anastomosis.
Of particular interest to the present invention, needles and other access tubes may be percutaneously attached to an implanted port in several ways. Implantable ports often include a needle-penetrable septum which permits the percutaneous penetration of a needle into the internal chamber. The chamber, in turn, is connected to one end of the implanted catheter, and the other end of the catheter is indwelling in or otherwise attached to the blood vessel. Instead of a septum, the use of needle-actuated valve mechanisms in subcutaneously implanted ports has also been proposed. See, for example, U.S. Pat. No. 5,527,278, and copending provisional application Ser. No. 60/036,124, filed on Jan. 21, 1997 (attorney docket no. 17742-000600), the latter of which is assigned to the assignee of the present invention and is incorporated herein by reference. Both the septum ports and valve ports are most commonly provided in single-port assemblies, thus requiring two separate valve ports to establish access for blood extracorporeal circulation. The use of dual-port assemblies for establishing both blood access and blood return has also been proposed. See, for example, FIGS. 3 and 4 in U.S. Pat. No. 5,527,278.
A rare but serious risk in performing hemodialysis and other extracorporeal blood circulation procedures results from accidental disconnection of the blood return needle from the implanted blood return port. Because blood is usually returned to the patient on the low pressure, venous side of the vasculature, the extracorporeal circulation system (e.g., a dialysis machine) will not necessarily be able to detect any pressure change if a venous return needle is accidentally dislodged and lost from the patient's vein. The pressure sensed by the extracorporeal circulation system results primarily from the needle itself, so alarms built in to the circulation system are usually insufficient. Thus, since blood will continue to be drawn from the arterial side of the vasculature, the patient is at significant risk of losing large amounts of blood and even death.
For these reasons, it would be desirable to provide apparatus, systems, and methods which will reduce the risk of continued blood withdrawal during extracorporeal blood recirculation protocols in the event that the blood return needle or device becomes dislodged. In particular, it would be desirable to provide implantable port assemblies where the blood access or supply port is automatically closed in response to loss of the needle from the blood return port. Such assemblies could be in the form of dual port valve assemblies present in a single base or enclosure, or could be in the form of separately implantable single port valve assemblies where mechanical, fluid, or other coupling is provided for the interlock. The interlock provided will preferably be simple, reliable, and operate in a fail safe manner. Optionally, the port assemblies and methods may also provide for closure of the blood access port and the blood return ports on loss of the either the blood return needle or the blood access needle from the patient. At least some of the above objectives will be met by the different aspects of the present invention discussed below.
2. Description of the Background Art
Dual port vascular access assemblies are described in a number of U.S. Patents. U.S. Pat. Nos. 5,527,278; 5,527,277; 5,503,630; 5,476,451; 5,417,656; and 5,281,199, describe a dual port assembly suitable for performing hemodialysis. U.S. Pat. No. 4,108,173, describes dual port assemblies for withdrawing or introducing fluids from a single vessel. U.S. Pat. Nos. 5,399,168; 5,360,407; 5,167,638; and 4,692,146, describe dual port assemblies which are connected to blood vessels through a common lumen.